Amiga 2000 Rev 4.3 - Only 0,5MB ram visible (0MB other RAM)

[snifferman]

Hello,
I got A2000 after baterry lekage. I replaced CPU socket, ROM socket,RTC chip, fixed 2 traces near CPU. Amiga works now, but only 0,5MB chip is visible in DIAGROM or AmigaTestKit(no slow ram/other ram). J101 on position 1-2, J102-closed, J500-closed.

I swaped Agnus to 8372A(was 8371). J101 on position 2-3, J102-open, J500-open. Still only 0,5MB chip is visible. No other ram.
I have tested U540,U541,U103,U104,U105,U106,U900,U603 on my TL866 programer. All ok.
I swaped chips from A500 (2xCIA,PAULA,DENISE,AGNUS,GARY,CPU). No change

Amiga works. I have installed TF536 on it and started Frontier and Setllers form SD card. Works fine.
Why i can`t get 1MB CHIP or 0,5MB CHIP+ 0,5MB SLOW?

EDIT:
Forgot to say, that i tested with KICK1.3, Kick3.1

mobo.jpg

bat and cpu.jpg

BAT region.jpg

[Maximilian]

That should work.

First question, did you have 0,5 MB chip and 0,5MB fast (ranger) ram to start with?
If yes, then please post closeups of the jumper areas
Make sure to measure the cuts you made to the jumper pads.

Have a look at this for the correct changes:
https://www.nightfallcrew.com/30/09/201 ... m-upgrade/

Only the 68000, Gary, Agnus and the ram are involved, changing anythig else is futile IMHO.

p.s. those are Sanyo LM33256G-15 chips?
(please look at them closely)

[snifferman]

Thank You for replay.

I have the same board revision as on this movie and there is a ranger RAM visible and 1MB of chip after mod.


I can se only 0,5MB of chip. Before the mod and after.
I checked the jumper pads with multimeter after cutting and they are separated.
I traced J500 to GARY and after cutting _EXRAM is +5v. 0V if bridged so it works correctly
Memory chips are SANYO LM33256G-15

Someone has schematic for REV 4.3? I found only one for REV6 and there RAM is in different chips.
How Ram is Detected on AMIGA 2000? Maybe some traces are still bad and preventing detection of other 512KB?

a3.jpg

a2.jpg

a1.jpg

[Maximilian]

Take a look at this one for the schema:
http://tele-work.hu/Vas/Amiga%20500%20T ... erence.pdf

[snifferman]

One of the RAM chips was bad.

after replacing it, 1MB chip is visible and no errors in memory test.

Thx for help.

[Maximilian]

Nice find!
Thanks for letting us know :)

[Dlfrsilver]

I would advise you to replace the CPU socket if not done already. The gunk goes under the socket. This is a common pb on A2000 that had battery leakage.

[FuzzyNormal]

One of the RAM chips was bad. After replacing it, 1MB chip is visible and no errors in memory test.

I have this exact problem with the Chip RAM only registering ~5MB when it should be 1MB.

In you situation, which chip was at fault, and what was the solution? I'm ignorant about this sort of stuff, and I'm unclear what the process is to "replace" a chip on the motherboard.

Would like to know if you could share!

Cheers